From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756417Ab0IHWPw (ORCPT ); Wed, 8 Sep 2010 18:15:52 -0400 Received: from terminus.zytor.com ([198.137.202.10]:39727 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756167Ab0IHWPs (ORCPT ); Wed, 8 Sep 2010 18:15:48 -0400 Message-ID: <4C880B12.3040200@zytor.com> Date: Wed, 08 Sep 2010 15:15:46 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.8) Gecko/20100806 Fedora/3.1.2-1.fc13 Thunderbird/3.1.2 MIME-Version: 1.0 To: Nick Lowe CC: linux-kernel@vger.kernel.org Subject: Re: Promoting Crusoe and Geode Processors to i686 Status References: <4C880278.3060108@zytor.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/08/2010 03:14 PM, Nick Lowe wrote: > Hi, > > Here goes... > > -mtune tunes the binary for given architecture. This as opposed to > defining the baseline architecture, and thus available instruction > set, which -march does. > > I believe that -mtune is predominantly used for instruction > scheduling. GCC uses it when it's reordering instructions to optimise > for specific micro-architecture over others. > > With -mtune=i686, I am of the opinion that you instruct the compiler, > and give it the opportunity, to deliver a better ordering of the > instructions. In this case, better ordering for i686 than you would > get with -mtune=generic32. > > I'm probably wrong somehow, it's probably marginal, and I'll concede > to your infinitely better knowledge any day! That's why I phrased it > as a question! :) > We don't pass -mtune=generic32 to gcc. We pass -Wa,-mtune=generic32 to gcc, which affects binutils only. -hpa